Generally, a speaker converts electrical signals to vibration of a vibration plate and creates waves in the air to generate an acoustic wave. That is, a speaker is a kind of a conversion device which converts electrical signals to an acoustic energy. A speaker includes vibration parts such as a vibration plate, support parts such as a damper, magnetic parts such as a magnet. A speaker may be classified into various categories based on a vibration plate position, a vibration plate shape, a principle/method for converting electrical signals to acoustic waves or the like. Especially, a speaker adapted to a display apparatus such as TV or the like is usually a radiation type speaker having a vibration plate positioned in the air. In the radiation type speaker, electric currents corresponding to acoustic signals are flowing in a coil provided in a magnetic field formed by a magnet and then the coil vibrates based on the intensity of electric currents, which is a common principle of a speaker operation.
Recently, a large screen display apparatus has been used broadly due to development of a semiconductor technology. To present a beautiful and simple design of such a large screen display apparatus as a FPD (Flat Panel Display), a speaker has to be small and slim. If a speaker is small, inner parts such as a vibration part, a magnet part and a support part should be minimized as well. However, if a speaker is small, functions of a speaker may deteriorate. This is due to deterioration of sound radiation efficiency caused by reduction of a vibration part, especially effective vibration area, flux density reduction caused by reduction of a magnetic part and so on. However, in spite of a small size of a speaker, a speaker for a large screen display apparatus is required to have the same as or better function than a conventional speaker.
In a speaker adapted to a FPD, it is not relatively easy to adjust a width and thickness of a speaker, while it is relatively easy to adjust a length of a speaker. Thus, it is general to reduce the width/thickness and increase the length in order not to reduce an effective vibration area. That is, a speaker having a rectangular or an oval shape with a short width and long length (hereinafter, a trade type speaker) is used not to reduce a work vibration area. That is, the speaker for a FPD has a high ratio of a long diameter to a short diameter, or a ratio of the length to the width of a speaker.
Referring to FIGS. 1 and 2, a conventional track type speaker will be described.
A speaker 3 includes an energy conversion part 40 and 50 that converts an electrical energy (an electrical signal) to a kinetic energy, and a vibration plate 20 that converts the kinetic energy generated at the energy conversion part 40 and 50 to an acoustic energy.
The energy conversion part 40 and 50 includes a fixing part 50 and a motion part 40 relatively moved with respect to the fixing part 50 by an electromagnetic force. The vibration plate 20 is connected to the motion part 40 to reproduce a sound by using the vibration of the vibration plate 20.
More specifically, the fixing part 50 is provided at a predetermined portion of a base frame 70. The fixing part 50 includes a permanent magnet 56. Commonly, an upper plate 52 and a lower plate 54 are provided on an upper portion and lower portion of the permanent magnet 56, respectively to concentrate a magnetic flux generated at the permanent magnet 56 there between. The motion part 40 is generally called as a voice coil assembly, which includes a bobbin 42 having a cylindrical shape and a voice coil 44 wound around the bobbin 42. The vibration plate 20 is connected to the bobbin 42. A center cap 29 is provided on a center of the vibration plate 20. The numeral reference 34 is a gasket.
A lower portion of the bobbin 42 is elastically connected to the base frame 70 by a damper 60. The vibration plate 20 is connected to an upper portion of the bobbin 42 and an outer end of the vibration plate 20 is connected to the base frame 70 by an elastic support part 30 (hereinafter, an edge). The damper 60 and the edge 30 are kinds of the supporting parts, which supports the vibration part including the voice coil 44, the bobbin 42 and the vibration plate 20 in their appropriate position to perform a vertical motion, in other words, a piston motion. Also, the damper 42 and the vibration plate 20 affects reproduction of high power and high quality sound.
As mentioned above, the trade type speaker 3 is shaped with a narrow width and a long length. The vibration plate 20 has a large ratio of a length to a width. However, the section of the bobbin 42 has a circular shape. Also, the shape of the damper corresponds to the shape of the bobbin and thus is circular, more specifically, annular. As shown in FIG. 3, the damper 60 elastically supporting the bobbin 42 has a ring shape and is repeatedly curved a predetermined distance in a circumferential direction from a hollow part 61. That is, the damper 60 has a plurality of wrinkle parts 61a in approximately concentric circle shape.
Referring to FIG. 2, an operation of the track type speaker will be described as follows.
Once electric currents are applied to the voice coil 44, an inductive force is generated at the coil within the magnetic field of the permanent magnet 56. Hence, the voice coil 44 moves vertically and the bobbin 42 connected to the voice coil 44 moves vertically. Accordingly, the vibration plate 20 coupled to the bobbin 42 also vertically moves in communication with the vertical motion of the voice coil 44, which is an upward/downward piston motion. That is, the vibration plate 20 vibrates forwardly/backwardly in communication with the voice coil 44 and the bobbin 42 to vibrate air, such that acoustic waves may be generated. The sound applied to the voice coil 44 as an electrical signal is substantially reproduced by the vibration of the vibration plate 20 to radiate outside of the speaker.